The slope of the lower bowl isn't steep enough while the slope up the upper decks is too steep, mainly because the two are separated by three levels of club seats/luxury boxes. About that...
The tri-level luxury seating makes upper deck seating feel as though it's not even connected to the building.
The scoreboard is probably the worst in the NFL.
Metal bleachers in the upper deck endzone give the place a cheap look.
Aside from that. it's great.
Seriously, take a drive across the state and visit the Linc. It cost about twice as much as Heinz Field but you get what you pay for. Way better sightlines and there's more of a flow to the seating architecture.